Insulator



Jan. 2, 1934. w A H|| EBRAND 1,941,749

INSULATOR Filed July 29, 1932 Fig? INVENTOR mmam A. Wmm'fld.

BY%% A ATTORNEY @5591. the insulator surface which are subjected to Patented Jan. 2, 1934 INSULATOR I I William A. Hillebrand, Barberton, Ohio', assignor to The Ohio Brass Company, Mansfield, Ohio,-.-a corporation of New Jersey 1 Y o Application July 29, 1932. Serial No.'6:2( i,(l62 I 4ClaimS. (ohm-s18) H f Thisinvention relates to electric insulators and particularlyto insulators of the suspension type, although itis applicable to insulators of other forms.

'One object of the invention is to prevent accumulation of conducting material on the sur face of the dielectric members in an insulator string; a

Another object of the invention is. to provide ielectric insulatorsof improved construction and operation.

Other objects and advantages will appear from the following description.

The invention is exemplified by the combina- ;tion and arrangement of parts shown in the accompanying drawing and described in the following specification, and it is more particularly pointed out in the appended claims.

In the drawing:

Fig. 1 is an elevation with parts in section of two units of a suspension string of insulators.

Fig. 2 is a top plan view of the upper unit shown in Fig. 1.

There are many parts of the world subject to .imore or less prolonged periods of dry weather.

In such localities, insulators used to support electrical transmission lines become coated with dust. It is a matter of experience that this dust coating tends to collect more heavily on those portions the greatest electrical stress.

The dust from practicaly all localities when dry is an excellent insulator. However, it generally contains soluble salts which, when the insulator becomes wetted by a fog, dew or light rain, form conducting electrolytes which may reduce the surface resistance of the insulator to a small fraction of one percent of its dry value. This reduction in surface resistance is often so low as to result in flashover at the operating voltage with consequent serious interruption to service.

The two essential elements in this reduction of surface resistance are dust containing soluble salts and moisture. Abundant experience proves that neither one of these alone, even when the moisture is a salt fog, will cause trouble. In some localities an important cause of contamination is soot particles deposited on the insulator surface with the fog itself.

If the dust particles can be kept from depositing on the insulator surface, a large part of the difficulty due to so-called wet leakage will be obviated.

The present invention provides an insulator for securing this result, one form of which is illustrated in. the accompanyingdrawing. The insu lator illustrated is .of a cap and pintype having, a dielectric member 10 made of porcelain or other;

vitreous material; a metal cap 11, and;a metal pin 12, all similar .tothe parts of standardinsul tor units exceptothat the porcelain shell v 1D ha s a smooth under surface at 13, and the cap, 11 is,- provided at its upper peripheral shoulderwithan; annular ring or, flange 14, which, is designed to reverse the direction, of the,electriclfluxconcenf tration from that which occurs in insulator strings,

as heretofore used. The flange 14 is provided with an opening or gap as shown in the drawing to permit coupling of the cap with the pin of the next adjacent insulator and to permit moisture to drain from the gutter formed on top of the cap by the flange 14.

In the present conventional type of suspension insulator, the dielectric member is usually provided with downwardly extending petticoats which extend downwardly toward thegnext lower unit, the cap of which is provided with an extended smooth surface. In view of the fact that porcelain has a specific inductive capacity approximately six times that of air, it is obvious that there will be a concentration of electric flux from the petticoats of the dielectric member to the large smooth surface of the insulator cap below. The flux will be concentrated at the tips of the petticoats but will be spread out over the surface of the cap. It is found that dust accumulation is greatest on those surfaces where the electric field is a maximum and that dust particles carried by the wind across the insulator string are drawn toward the lower porcelain surfaces into those regions where the electric field is a maximum. This causes accumulation of dust on the lower surface of the dielectric member, which action is augmented by eddy currents set up in the pockets between the petticoats.

In the present invention as shown in the drawing, the parts are so arranged with respect to one another that the direction of electric field concentration is now reversed, and is a maximum on the cap below and a minimum on the porcelain above. With this arrangement, dust particles which are being carried across the insulator by the wind are drawn downwardly by the concentration of flux produced by the flange 14 toward the metal cap where they can do no harm, instead of being carried upwardly to the porcelain above.

Extensive experiments have also tended to show that ribs or petticoats on the dielectric member of conventional design result in air eddies which tend to carry dust upward and into the annular grooves in the porcelain, facilitating the deposit of dust upon the porcelain surface. In the present invention, the smooth under surface 13 not only prevents concentration of flux on this surface but also avoids the creation of eddy currents and permits the under surface to be swept clean bypassing currents of air. 'In the construction shown in the drawing, any air eddies would be downward toward the metal of the cap below where any deposit of dust can do no harm.

1. A suspension insulator comprising a dielectric member having a radiallyyprojecting flange, a boss at one side of said fian'geand a recess in said boss opening at the side of said flange opposite said boss, a cap secured to said boss and a pin secured in said recess, said cap having a peripheral ring at the upper shoulder portion thereof extending upwardly from said cap to formafiux c'ontrQLtendin'g to concentrate the electrostatic flu'x in the field about said insulator atth'e upperfextremityof said ring.

2.1 insulator string comprising a plurality of units-connected inseries, each unit comprising adielct'ric member having aradially extending flange with a smooth lowerxsurface, a cap secured to {said dielectric member at one side threo'f-anda pin'secured toisaid dielectric memberat 'theopposite side thereof, saidcap having a per heral ring projectingupwardly from the upperfshould'e'r portion of said cap and extending toward the smooth lower surface of the flange on the next higher insulator in the string to form a flux control for concentrating the flux at the periphery of said ring.

3. An insulator string comprising a plurality of units, each provided with a cap and a pin for securing said units together, saidunitseach having a radially extending flange of dielectric material provided with a smooth lower surface, each cap having an upwardly projecting ring at the upper shoulder portion thereof extending upwardly toward the lower surface of the dielectric flange on the next higher unit in the string, the upwardly projecting ring on each cap having a gspthere n to'permit moisture to drain from the gutter formed on top of the cap by said ring.

7 4. An insulator string comprising a plurality of units connected together in series, each unit com- :prising a dielectric member, a cap and a pin, the dielectric member having a radially extending 

